Problem with central locking, a sensor, wiring or microswitch

[pothole]

So, my '97 Box has developed a peculiar fault. It goes something like this.

Sometimes, when I unlock the car, the central locking will cycle twice. I'll then get into the car, turn the ignition key and it will cycle twice again. When this happens, the light on the door lock switch on the dash will turn on and remain on. Pressing it cause the locks to cycle twice, again.

Also, the window auto-drop feature on the passenger that activates when you partly pull the door release on the inside or the outside will stop working (the actual window lifter appears to work normally at all times). And even more bizarrely, as you drive along, occasionally the locking will suddenly cycle twice and at the end you get two short toots from the horn and the interior lighting turns on for about three seconds.

What's even weirder, is that it only does this intermittently. Sometimes everything works 100% fine, including passenger side window auto drop.

One other further factor. This all began around the time I had a DAB radio wired in. Now I think I noticed a little weirdness before the DAB was fitted, but I'm not 100% clear. The DAB radio fitting involved a little control unit that hooks into the loom under the centre console and feeds the stereo via the FM-in. It also had an aerial wired in up the passenger A pillar.

At the moment my instinct is to have the DAB removed, but it's just possible the issues started before the DAB was fitted.

Thoughts, anyone?